The present invention relates to a technique for wire bonding and more particularly to a technique effective for use in a wire bonding process in assembling a semiconductor integrated circuit device using an insulated wire.
In the fabrication of a semiconductor integrated circuit devices, the process of wire bonding is known which wires conductive metal wires for connecting a plurality of electrodes for external connection disposed on a semiconductor chip on which predetermined integrated circuits are formed to a plurality of leads functioning as terminals for external connection when the semiconductor chip is mounted.
To meet the increasing demands of late for higher packaging density and smaller size of semiconductor integrated circuit devices, the density of the externally connected electrodes is increasing greatly, and hence, the spacing between the bonding wires and diameter of the bonding wires is decreasing. As a result, problems arise such as the occurrence of short circuiting between bonding wires and abnormalities due to deterioration in rigidity of the bonding wire.
To cope with such problems, it is known in the art of wire bonding to use, an insulated wire formed of a metallic core wire covered with an insulating film.
In the well known ball bonding technique, the end of a wire passed through a bonding tool such as a capillary is melted and formed into a ball and then bonded to a contact area. But in the bonding of the wire to the side of a lead, an area of the peripheral surface of the wire covered with an insulating film is compression-bonded to the surface of the lead. Therefore, it is expected that the bonding strength is lowered, the electric resistance is increased, and reliability of the bonding is lowered.
In view of these problems, there have been disclosed improved methods for wire bonding using an insulated wire, particularly for the bonding to the side of the lead, in Japanese Laid-open Patent Publication Nos. 62-140428 and 62-104127.
The former improved method is such that the pressure provided through the bonding tool, when an insulated wire is bonded to the lead side, is progressively increased in multiple steps so that the nonconductive insulating film existing between the core wire of the insulated wire and the lead is removed and thereby a reliable bond is obtained.
The latter improved method is such that when a capillary with the insulated wire is passed therethrough when an insulated wire is bonded to the lead side, the wire is heated and also given vibration so that the insulating film existing between the core wire of the insulated wire and the lead is removed and thereby a reliable bond is obtained.